Method of refining crude oils having organic acidity

ABSTRACT

The invention relates to a method of refining crude oils having high acidity by neutralising the organic acidity thereof. The inventive method consists in adding a nitrogenous compound to the crude oil. Said method is characterised in that a nitrogenous compound containing at least three carbon atoms, a secondary amine group and a hydric group is introduced at at least one point of the crude oil pre-treatment units upstream of, or in the atmospheric distillation unit.

[0001] The present invention relates to a process for refining crude oils having high organic acidity.

[0002] The crude oils or fractions thereof having high acid contents are principally those containing naphthenic acids. It is known that these crude oils present risk of corrosion during extraction on the oil field, when they are transported, as well as during their refinement. The petrol industry and the refining industry must find the means to increase the value of these crude oils without being obliged to develop new technologies to protect devices and machinery for transporting these crude oils or fractions thereof or also for treating them whether it be on the field, in maritime transport or by rail, in pipes or in the refinery. This crude oil acidity is usually measured by the TAN number or index (Total Acid Number), which is measured by potentiometric analysis in accordance with the standard ASTM D664 and by colorimetry with the standard D974. Thus a discount is applied to the crude oils as a function of the TAN index: the price of the crude oil depends on the value of this acidity. Now today, most of the crude oils extracted are acidic by nature, that is to say that they contain corrosive compounds like the sulphurated derivatives but also naphthenic acids. It can be understood why the development of a process for treating these crude oils which allows the obtention of a weak acidity in the entirety of the crude oil or in the different carbonized cuts composing it would be beneficial: it would allow both the increase of refining margins as well as the limitation of the risk of corrosion which is a generator of additional expenses in the case of perforations in storage, transport or processing equipment, particularly in refineries. Numerous efforts have been made in the past years to develop such a process of deacidification or of neutralisation of crude oils.

[0003] Amongst the different ways which have been retained, neutralization by nitrogenous compounds, either combined or not combined with the use of a solvent, has been mentioned particularly in the U.S. Pat. Nos. 2,769,768, 3,176,041, -2,911,360, 4,634,519 or 5,550,296.

[0004] The patent U.S. Pat. No. 2,769,768 describes the use of a linear or branched primary alcohol having from 4 to 7 atoms of carbon with a mixture formed from methanol and from ammonia to neutralize and remove the heavy naphthenic acids from a deparaffinated hydrocarbon oil.

[0005] The U.S. Pat. No. 3,176,041 proposes trapping the naphthenic acids of a crude oil by contact with a clay impregnated with a volatile amine having a boiling point below 100° C., particularly ammonium hydroxide. This process is not applicable in the crude oil production field, nor even in the refinery as a contact temperature above 200° C. is required for 20 to 75 minutes and the extremely complex daily regeneration of several hundred tons of clay.

[0006] The U.S. Pat. No. 2,911,360 describes a process which is applied to a crude oil. The crude oil is deacidified in liquid phase by bringing it into contact with a base in the presence of an alcohol, then distilled. The base can be ammoniac while the solvent phase is an aqueous solution containing from 30 to 50% by weight of alcohol. The naphthenic acids recovered by distillation are regenerated after acidification in the sulphuric acid of the extraction solvent. This process is difficult as it involves two treatments, one in the liquid phase and one in the vapour phase. Moreover it is only applicable in the refinery as it involves atmospheric distillation and distillation under vacuum of the treated crude oil.

[0007] The patent U.S. Pat. No. 4,634,519 describes a deacidification process of oil cuts using a specific solvent mix, comprising water, methanol and ammoniac. It concerns extracting the naphthenic acids. This process is applied solely to oil cuts because applying this treatment to a crude oil has lead to a stable emulsion rendering the recovery of the extraction solvent practically impossible.

[0008] The U.S. Pat. No. 5,550,296 describes the synthesis of ketones, but also describes a process for deacidifying crude oil directly when it comes out of the well in an oil field, before stabilization of the crude oil, with liquid ammonia to neutralize the naphthenic acids. Such a process cannot be implemented as it is in the refinery.

[0009] For the specific treatment of oil cuts of the type obtained by refining the crude oil, taken separately, it has often been proposed to use nitrogenous compounds of the monoalkyl or monoarylamine type, optionally polymers of these amines, of monoalkanolamine, and even of tetraalkylised ammonium hydroxide as it is described in the U.S. Pat. No. 4,589,979, U.S. Pat. No. 4,752,381, U.S. Pat. No. 4,827,033, U.S. Pat. No. 5,683,626, and EP 0924286A2.

[0010] None of the above documents either teaches or suggests the invention which is here applied essentially to crude oil which is not yet distilled.

[0011] The aim of the present invention is to convert into amides, the organic acids contained in a crude oil having high acidity, principally the naphthenic acids, during standard refining of this crude oil in the refinery. The distilled fractions thus neutralized, are no longer the causes of major corrosion phenomena in the equipment through which it passes. Moreover these cuts can even be made more valuable, this treatment having the effect of favouring the appearance of amide functions which improves the qualities of the products marketed. Thus the addition of lubricity additives to gasolines and middle distillates, kerosene and gas oil can be limited, this lubricity function in fact already being present within the distilled cut.

[0012] A subject of the present invention is therefore a process for refining by neutralization of the organic acidity of crude oils having strong acidity consisting of adding a nitrogenous compound to said crude oil, said process being characterized in that, a nitrogenous compound comprising at least three carbon atoms, a secondary amine group and a hydroxylated group is introduced into at least one point in the oil pretreatment unit upstream of, or in the atmospheric distillation unit.

[0013] Such compounds have the advantage of being able to react at low temperature particularly to neutralise the napthenic acids in amine salts, the amide formation being carried out by increasing the temperature of the crude oil before its distillation. The amine salts which result from the naphthenic acids remain in the crude oil both during the crude oil preheating operations and during the desalting operations, progressively being converted into amides. Thus they are always present but in the amide form in the crude oil when it enters into the atmospheric distillation furnace. Because of this the naphthenic acids thus amidified and the other amides optionally formed from other acid compounds present are distilled like the other hydrocarbons and are found in the different cuts distilled in the usual way. It is found advantageously that these amides confer upon the distilled cuts unexpected properties of lubricity and of anti corrosion. Thus it has thus been seen that at the head of the tower it was possible to limit or even to omit the addition of neutralising amines. In addition, the cuts of middle distillates for the production of gas oils have a greatly reduced acidity and improved lubricity.

[0014] To obtain such results, the nitrogenous compounds used are chosen from the compounds of formula (I) below

[0015] in which Y is a linear or branched alkyl group comprising from 1 to 10 carbon atoms, optionally hydroxylated, and Z is chosen from the alkyl, hydroxyalkyl and polyhydroxyalkyl (containing up to 6, preferably up to 4 hydroxy), primary, secondary or tertiary amine groups and their hydroxylated and polyhydroxylated derivatives, the alkyl functions of these groups comprising from 1 to 10 carbon atoms.

[0016] In a first preferred embodiment of the invention, a compound of formula (I) is used in which Z is a group chosen from the hydroxyalkyl and polyhydroxyalkyl groups.

[0017] The compounds of formula (I) preferred in this first embodiment are chosen from the dialkanolamines of the group constituted by diethanolamine, dipropanolamine, dibutanolamine, N-propanol-2-ethanolamine, N-butanol-2-ethanolamine, N-butanol-3-ethanolamine, N-butanol-2-propanolamine, N-butanol-3-propanolamine, N-propanol-2-butanolamine, di-(methyl 1-hydroxy2)-propylamine, diisopropanolamine and di-(methyl2hydroxy2)-butylamine.

[0018] For optimal effectiveness of the process according to the invention, the preferred compounds are chosen from diethanolamine and diisopropanolamine.

[0019] In a second embodiment of the invention, a compound of formula (I) is used in which Z is an alkyl group comprising from 1 to 5 carbon atoms.

[0020] The compounds of formula (I) are chosen from N-methyl-ethanolamine, N-propyl-ethanolamine, N-butylethanolamine, N-isobutylethanolamine, N-pentylethanolamine, N-methylpropanolamine, N-isopentylethanolamine, N-propyl-propanolamine, N-butylpropanolamine, N-isobutylpropanolamine, N-pentylpropanolamine, N-isopentylpropanolamine, N-methyl-butanolamine, N-propyl-butanolamine, N-butylbutanolamine, N-isobutyl-butanolamine, N-pentylbutanolamine, N-isopentylbutanolamine, N-methyl-pentanolamine, N-propyl-pentanolamine, N-butylpentanolamine, N-isobutylpentanolamine, N-pentylpentanolamine and N-isopentylpentanolamine. In an optimal embodiment, N-propylethanolamine and N-isobutylethanolamine are preferred as compounds of formula (I).

[0021] In a third embodiment of the invention, a compound of formula (I) is used in which Z is chosen from the amine primary, secondary and tertiary amine groups and their monohydroxylated and polyhydroxylated derivatives.

[0022] The preferred compounds in this third embodiment are chosen from the group constituted by N-hydroxy-2-ethylhydrazine, N-hydroxy-2-ethylethylenediamine, N-hydroxy-2-ethyl-(1-3)propylenediamine, N,N′-bis(dihydroxy-2,3-propyl)amine and hydroxy-2-(1,3)propylenediamine-Preferably N-hydroxy-2-ethylethylenediamine will be chosen.

[0023] In order to neutralise then amidify the organic acids of the crude oil to be refined, the compound of formula (I) can be introduced before the crude oil desalting unit, when preheating of the desalted crude oil is underway, preferably before the preheaters or also in the still tower.

[0024] Another subject of the invention is the application of the process to the neutralisation of the organic acids contained in the crude oils having acidity higher than 0.5 mg KOH/g.

[0025] A third subject of the invention corresponds to the oil cuts obtained by applying said process according to the first subject of the invention.

[0026] Amongst these oil cuts there are the middle distillates with a cut temperature comprised between 150 and 400° C.

[0027] A second type of cut corresponds to the cuts which are called light with cut temperatures comprised between the starting point and 150° C. and with acidity below 0.5 mg of KOH/g.

[0028] The invention will now be described on the basis of examples given below intending to illustrate the characteristics of the invention but without wishing to limit its scope.

EXAMPLE I

[0029] The present invention describes the process for conversion of organic acids of a crude oil with nitrogenous compounds according to the invention.

[0030] A crude oil A with moderate acidity (12.9 mmoles of carboxylic acid/l of crude oil) is used on the one hand and a crude oil B with high acidity (68.1 mmoles of carboxylic acid/1 of crude oil) is used on the other hand. 201 of crude oil and the compound of formula (I) here diethanolamine (or DEA) are introduced into an agitated reactor. The crude oils A and B thus complemented are then subjected to infrared analysis. It is found that the acid peak disappears at 1708 cm⁻¹ in the two crude oils A and B. There has thus been a conversion of the carboxylic acids to carboxylic acid salt. Then the temperature of complemented A and of B is raised to 150° for 30 minutes in order to amidify these salts.

[0031] These crude oils thus amidified are then introduced into a distillation pilot. The thus distilled oil cuts are then subjected to infrared analysis. These different cuts are compared with the identical cuts of the pure crude which is not treated but distilled in the same distillation pilot plant. It is found that in these cuts the carboxylic acids have indeed disappeared and that amide compounds have indeed been formed.

[0032] The details of the distilled cuts are given in the Table (I) below. The results are given in mmoles of carboxylic acid per litre of hydrocarbons. TABLE I A B Without With DEA Without With DEA Weight of 0 52 g 0 275 g added DEA  PI-150 0 0 0 0 150-230 15.2 3 0 0 230-350 32.7 11.4 34.8 11.5 350-400 29.2 14 94.2 40.1 400+ 0 0 15 9

[0033] From this table established by analysis of the graphs obtained by infrared analysis it is seen that in all the cuts obtained from the treated product before distillation, a notable reduction in the carboxylic acid content and thus in corrosive chemical species is observed. This is particularly true for the gas oil cut, distilled between 230 and 350° C. in which the majority of naphthenic compounds are concentrated.

EXAMPLE II

[0034] The present example aims to describe the advantages linked to the process as regards the improvement in lubricity of the middle distillate cuts and the anticorrosive effect of the amides formed in the light distillation cuts.

[0035] Thus the 230-350° C. cuts from Example I with and without amide formation before distillation are taken up and the lubricity of each one of them is measured by the method known as BFRR (High Frequency Reciprocating Ring), according to the standard EC121561. It is expressed by Wear Scare Diameter (WSR) in μm. A correct lubricity leads to wear diameter values below 460 μm. The smaller this value is, the better is the lubricity.

[0036] The results are given in Table II below. TABLE II A B Cut Without With DEA Without With DEA Acidity (mmole COOH/1) 32.7 11.4 34.8 11.5 Lubricity (μm) 255 265 292 310

[0037] The results show that, although the carboxylic acids and in particular the naphthenic acids have a role that is well known in improving lubricity, the disappearance of these acids by amidifying them does not have a harmful effect on the lubricity. The effect of the acids as an improver of lubricity of the gas oil cut (230-350° C.), in particular that of the crude oils having strong organic acidity (B), was replaced by the effect of the corresponding amide.

EXAMPLE III

[0038] The present example aims to show the progressive character of the reaction of the alkanolamines in particular of the diethanolamine (DEA) on the crude oil B with acidity corresponding to a TAN of 4.47 or 68 mmole/l of acidity measured.

[0039] To monitor the reaction, 434 g of crude oil B and 13 ml of DEA diluted to 40% by weight in water are introduced into a 500 ml flask. DEA is gradually added over 50 minutes while stirring the mixture with a standard magnetic stirrer.

[0040] This addition is followed by a heating of the crude oil B to 100°, then to 150° C. for 30 minutes. The temperature is then stabilized at 180° C. after 2 hours.

[0041] The reaction is monitored in crude oil while DEA is added by IRFT spectrometry using a measuring stick dipped in the crude oil B forming a part of the REACT IR spectrometry marketed by the company METTLER. Periodically during this reaction the infrared spectrums of the product contained in the flask are measured.

[0042]FIGS. 1 and 2 give a representation of the evolution of the infrared spectrums during the addition of DEA and during the heating in relation to time.

[0043]FIG. 1 presents, three dimensionally, the disappearance of the acid derivatives (band centred on the wavelength 1710 cm⁻¹), the appearance of amine salts (band centred on 1560 cm⁻¹) and the appearance of the amides (band centred on 1650 cm⁻¹).

[0044]FIG. 2 represents, in two dimensions, in relation to time, the formation of amide (band centred on 1650 cm⁻¹) after addition of DEA and the maintenance of crude oil B at 140° C. for one hour. The formation of esters in a small quantity linked to the presence of water brought on by the addition of DEA (band centred on 1740 cm⁻¹) is also noted. 

1. Process for refining by neutralisation of the organic acidity of crude oils having high acidity consisting of adding a nitrogenous compound to said crude oil, said process being characterized in that there is introduced in at least one point of the unit of pretreatment of crude oil upstream of or in the unit of atmospheric distillation a nitrogenous compound comprising at least three carbon atoms, a secondary amine group and a hydroxylated group.
 2. Process according to claim 1 characterized in that the nitrogenous compounds used are chosen from the compounds of formula (I) below

in which Y is a linear or branched alkyl group comprising from 1 to 10 carbon atoms, optionally hydroxylated, and Z is chosen from the alkyl, hydroxyalkyl, and polyhydroxyalkyl, primary, secondary or tertiary amine groups and their hydroxylated and polyhydroxylated derivatives, the alkyl functions of these groups comprising from 1 to 10 carbon atoms.
 3. Process according to claims 1 and 2 characterized in that in the compound of formula (I), the Z is a group chosen from the hydroxyalkyl and polyhydroxyalkyl groups.
 4. Process according to claims 1 to 3 characterized in that the compound of formula (I) is chosen from the group constituted by diethanolamine, dipropanolamine, dibutanolamine, N-propanol-2-ethanolamine, N-butanol-2-ethanolamine, N-butanol-3-ethanolamine, N-butanol-2-propanolamine, N-butanol-3-propanolamine, N-propanol-2-butanolamine, di-(methyl 1-hydroxy2)-propylamine, diisopropanolamine and di-(methyl2hydroxy2)-butylamine.
 5. Process according to claim 4 characterized in that the compound of formula (I) is chosen from diethanolamine and diisopropanolamine.
 6. Process according to claims 1 and 2 characterized in that in the compound of formula (I), Z is an alkyl group comprising from 1 to 5 carbon atoms.
 7. Process according to claim 6 characterized in that the compound of formula (I) is chosen from N-methyl-ethanolamine, N-propyl-ethanolamine,N-butylethanolamine, N-isobutylethanolamine, N-pentylethanolamine, N-methyl-propanolamine, N-isopentylethanolamine, N-propyl-propanolamine, N-butylpropanolamine, N-isobutylpropanolamine, N-pentylpropanolamine, N-isopentylpropanolamine, N-methyl-butanolamine, N-propyl-butanolamine, N-butylbutanolamine, N-isobutyl-butanolamine, N-pentylbutanolamine, N-isopentylbutanolamine, N-methyl-pentanolamine, N-propyl-pentanolamine, N-butylpentanolamine, N-isobutylpentanolamine, N-pentylpentanolamine and N-isopentylpentanolamine.
 8. Process according to claims 6 and 7, characterized in that the compound of formula (I) is chosen from N-propylethanolamine and N-isobutylethanolamine.
 9. Process according to claims 1 and 2 characterized in that in the compound of formula (I), Z is chosen from the primary, secondary and tertiary amine groups and their monohydroxylated and polyhydroxylated derivatives.
 10. Process according to claim 9 characterized in that the compound of general formula (I) is chosen from the group constituted by N-hydroxy-2-ethylhydrazine, N-hydroxy-2-ethylethylenediamine, N-hydroxy-2-ethyl-(1-3) propylenediamine, N,N′-bis(dihydroxy-2,3-propyl)amine and hydroxy-2-(1,3)propylenediamine.
 11. Process according to claims 9 and 10 characterized in that the compound of formula (I) is N-hydroxy-2-ethylethylenediamine.
 12. Process according to claims 1 to 11 characterized in that the nitrogenous compound is introduced before the crude oil desalting unit, during preheating of the desalted crude oil, preferably before the heat exchangers or also in the distillation tower. 13 Process according to one of claims 1 to 12 in which the crude oils have an organic acidity and total acidity higher than 0.5 mg KOH/g. 